Methods for substantially equalizing rates at which material is removed over an area of a structure or film that includes recesses or crevices

ABSTRACT

Methods for preventing isotropic removal of materials at corners formed by seams, keyholes, and other anomalies in films or other structures include use of etch blockers to cover or coat such corners. This covering or coating prevents exposure of the corners to isotropic etch solutions and cleaning solutions and, thus, prevents higher material removal rates at the corners than at smoother areas of the structure or film from which material is removed. Solutions, including wet etchants and cleaning solutions, that include at least one type of etch blocker are also disclosed, as are systems for preventing higher rates of material removal at corners formed by seams, crevices, or recesses in a film or other structure. Semiconductor device structures in which etch blockers are located so as to prevent isotropic etchants from removing material from corners of seams, crevices, or recesses in a surface of a film or other structure at undesirably high rates are also disclosed.

FIELD OF INVENTION

The present invention relates generally to methods for wet etchingstructures or films and, more specifically, to methods for preventingisotropic removal of materials at corners formed by seams, keyholes, andother anomalies in the surfaces of structures or films opening ontoexposed surfaces of the structures or films.

BACKGROUND OF RELATED ART

When thin films are deposited in semiconductor device fabrication,seams, keyholes, and other anomalies that include corners at the exposedsurface of the film may be formed in the films above recesses in theunderlying device. Existing chemistries of isotropic etch (e.g., wetetch or cleaning) processes, such as hydrofluoric acid (HF) (e.g., 100:1water:HF), buffered oxide etchants (BOE) (e.g., 20:1 water:BOE), andetchants that include ammonium fluoride, dilute HF, and phosphoric acid,will enter the recesses or crevices of such anomalies and removematerial from corners of the structure or film bounding the recesses orcrevices at a faster rate than the material is removed from smoother(e.g., more planar), exposed, nonrecessed surfaces of the film or otherstructure. Such undesired amplification of anomalies may occur even whenfilms or other structures that include seams, keyholes, and otheranomalies have been polished or planarized, and even when such anomaliesare not visible by modern imaging techniques, such as electronmicroscopy. The increased rate at which material is removed by isotropicetchants from corners may result in amplification of seams, keyholes,and similar anomalies, which enhances the occurrence of nonplanaritiesin the topography of the etched film or other structure. This phenomenonis particularly undesirable in state-of-the-art semiconductor devices,in which circuit, or “line,” widths are about 50 nm or less. Thesedetrimental effects will continue to increase with continued decreasesin feature dimensions of state-of-the-art semiconductor devices.

While anisotropic etch (e.g., dry etch) processes may be used to avoidthe amplification of seams, keyholes, and similar anomalies into largersurface nonplanarities as material is removed from a structure or film,use of such processes undesirably increases processing time and costs.

Accordingly, wet etchants and wet etch processes that reduce, minimize,or eliminate amplification of seams, keyholes, and similar anomalies aredesired.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, in which various features of embodiments of the presentinvention are depicted:

FIG. 1 is a graph illustrating the isoelectric points (IEP—the point atwhich a molecule has no net electrical charge) of a variety ofmaterials;

FIG. 2 is a schematic representation of an embodiment of the presentinvention for preventing removal or decreasing the rate at whichmaterial is isotropically removed from corners of seams, crevices, orrecesses of a structure of a film;

FIG. 3 is a cross-sectional representation that illustrates theintroduction of etch blockers into recesses or crevices of a structureor film from which material is to be removed according to an embodimentof the present invention;

FIG. 4 is a cross-sectional representation showing the removal of theetch-blocker of FIG. 3 from undesired locations of a structure or filmaccording to an embodiment of the present invention;

FIGS. 5 and 6 are cross-sectional representations of the structure orfilm of FIG. 4 that illustrate the removal of material from thestructure or film with etch blockers within recesses or crevices of thestructure or film according to an embodiment of the present invention;

FIG. 7 shows the structure or film of FIG. 6, with material having beenremoved from smooth, nonrecessed surfaces thereof to about a lowermostlevel or elevation at which blockers are present, according to anembodiment of the present invention;

FIG. 8 shows the structure or film of FIG. 7, from which etch blockershave been substantially removed according to an embodiment of thepresent invention; and

FIGS. 9 through 15 are electron micrographs depicting variousembodiments of processes according to the present invention.

DETAILED DESCRIPTION

The present invention, in one embodiment, includes solutions, including,but not limited to, wet etchants and cleaning solutions, that areformulated, or configured, to prevent an etchant from isotropicallyremoving material from corners of seams, keyholes, and similar anomaliesopening onto exposed surfaces of films or other structures that are tobe etched or cleaned. As used herein, the term “etchant” includes, butis not limited to, chemicals and mixtures of chemicals that removematerial, by dissolution or otherwise; the term “wet etchant” includes,but is not limited to, etchant solutions; the term “etch,” inasmuch asuse of the term applies to wet etchants, includes, but is not limitedto, exposure of a film or structure from which material is to be removedto a wet etchant; the terms “isotropic removal” and “isotropic etch”refer to processes by which material is simultaneously removed from afilm or structure in a plurality of different directions; and the term“etch blocker” includes, but is not limited to, elements that mayprevent a region of a film or structure from being exposed to an etchantas smoother regions of the film or structure are etched. Etch blockersinclude particles and molecules, such as surface active agents (whichare commonly referred to as “surfactants”), that have molecular weightsor dimensions that facilitate their introduction into very smallrecesses or crevices, such as those of seams, keyholes, and otheranomalies, that may be present in a surface of a film or otherstructure.

The present invention includes etch blockers, etch systems, and methodsfor preventing, with some selectivity, wet etchants from isotropicallyremoving material from corners of seams, keyholes, and other, similaranomalies opening onto surfaces of films or other structures as materialis removed from the surfaces of the films or other structures byisotropic etch processes (e.g., with wet etchants).

The present invention also includes etch blockers that adsorbnonselectively to a structure from which material is to be removed toserve as diffusion barriers, as well as etch systems and methods thatemploy such diffusion barriers. In some embodiments, diffusion barriersmay decrease the rates at which reactive etch species are transported toor, more generally, otherwise become exposed to, a material to beremoved. Some embodiments of diffusion barriers may decrease the ratesat which products, including by-products, of an etching reaction areremoved.

Etch blocker-containing solutions, including wet etchants and cleaningsolutions, according to an embodiment of the present invention areconfigured to prevent the removal of material from corners of seams,keyholes, and similar anomalies in surfaces of films that are to beetched isotropically; i.e., more quickly the material is removed fromsmoother (e.g., more planar) regions.

The etch blocker of some embodiments of the present invention comprisesa particle or molecule with a molecular weight or dimensions thatfacilitate its preferential introduction into small recesses orcrevices, such as seams and keyholes, in a film or other structure thatis to be etched. The molecular weight or dimensions of the etch blockermay be large enough to plug a recess or crevice into which the etchblocker is introduced.

The etch blocker may be selected on the basis of its ability to adsorbto surfaces of anomalies of the film or other structure, for example, byvan der Waals bonding or by charge differences between the etch blockerand the material of the film (i.e., the mutual attraction that positivecharges and negative charges have for each other), and other types ofchemisorption, etc. Of course, when an etch blocker adsorbs to and coatsa surface that is to be shielded from an isotropic etchant, a singlemolecule or particle of etch blocker need not have dimensions sufficientto plug a recess or crevice.

Such an etch blocker may prevent isotropic removal of the material fromcorners or anomalies at undesirably high rates relative to the rates atwhich material is removed from surfaces of a structure or film bypreventing isotropic etchants from contacting (e.g., by adsorbing to,physically covering, etc.) material at corners of structure or film thatwould otherwise be exposed to the isotropic etchants.

In other embodiments, the etch blocker comprises particles or moleculesthat nonselectively adsorb to and coat at least a material that is to beremoved by etch processes, including both smooth features and anomalies.A non-selectively adsorbing etch blocker acts as a diffusion barrier,which may decrease the rates at which reactive etch species are exposedto a material to be removed, decrease the rates at which products,including by-products, of an etching reaction are removed, or slow bothof these types of diffusion.

The etch blocker may comprise a surfactant. When a surfactant isemployed as the etch blocker, it may be selected, at least in part, onthe basis of an isoelectric point of the material to be etched. FIG. 1is a graph that shows the zeta potentials of a variety of materials atdifferent pHs. The pH at which the zeta potential of a material is zerois the isoelectric point of that material. In addition, the surfactantmay be selected on the basis of the pH of the etch solution with whichthe etch blocker is to be used relative to the isoelectric point of thematerial to be removed. As an example, if a material to be removed hasan isoelectric point of about 2.5 and the etch solution selected toremove that material has a pH of less than about 2.5, an anionic (i.e.,negatively charged) surfactant may be used. As another example, if anetch solution having a pH of greater than about 2.5 is used to remove amaterial with an isoelectric point of about 2.5, the wet etchant ofwhich the etch solution is a part may also include cationic (i.e.,positively charged) surfactant.

Another embodiment of etch blocker includes a surface active polymer,which may be selected based on its ability to physically adsorb, or“physisorb,” to a particular material to be etched (e.g., silicondioxide). Specific embodiments of surface active polymers includepolyethylene glycol (PEG), polyvinyl pyrrolidine (PVP), and polyacrylicacid (PAA). When surface active polymers are used with an etchant havinga high ionic strength (e.g., BOE, etc.) the high ionic strength of theetchant will compress an electric double layer that includes chargedmolecules and charged surfaces, reducing the attractive forces that arerequired for such an etch blocker to adsorb to the material to beetched, and enabling the use of less ionic or non-ionic surfactants asand polymers.

In another embodiment, nonionic surfactants, which lack positive andnegative charges, may be useful as etch blockers regardless of theisoelectric point of the material to be removed or the pH of the etchsolution. Amphoteric surfactants, which include both positively chargedand negatively charged regions, may also be used as etch blockers of awet etchant according to a further embodiment of the invention.

ZONYL® FS-62, an anionic fluorosurfactant available from E. I. du Pontde Nemours and Company of Wilmington, Del., NOVEC® 4300 electronicsurfactant, an anionic fluorosurfactant available from the 3M Company ofMaplewood, Minn., and ammonium lauryl sulfate (ALS) are nonlimitingexamples of anionic surfactants that may be useful as an etch blocker ina wet etchant according to embodiments of the present invention. Cetyltrimethylammonium bromide (CTAB), also referred to as“hexadecyltrimethylammonium bromide,” is a nonlimiting example of acationic surfactant that may be useful in a wet etchant according toembodiments of the present invention. TRITON® X-100, a nonionicsurfactant having the chemical formula C₁₄H₂₂O₂(C₂H₄O)_(n), with ahydrophilic polyethylene oxide group (on average it has 9.5 ethyleneoxide units) and a hydrocarbon lipophilic or hydrophobic groupcomprising a 4-(1,1,3,3-tetramethylbutyl)-phenyl group, and availablefrom Union Carbide Corporation of Houston, Tex., is an example of anonionic surfactant that may be included in a wet etchant of embodimentsof the present invention.

According to another embodiment, the etch blocker may be a particulateetch blocker that does not adsorb to, but has a configuration anddimensions that facilitate its receipt within recesses or crevices of anexposed surface being etched, either passively or with some action(e.g., vibration, a small amount of turbulence in the solution, etc.).Without limiting the scope of the present invention, such an etchblocker may be geometrically optimized (e.g., rounded, etc.) tofacilitate its introduction into recesses or crevices, configuredsomewhat complementarily to the recesses or crevices within which it isto be received, modified to have a tailored steric hindrance, orotherwise modified, as may facilitate introduction and/or retention(e.g., when pressure waves are used to remove etch blocker from smoothersurfaces of the structure or film to be etched) of the etch blocker intothe recesses or crevices.

An etch blocker-containing solution of the present invention may beconfigured to facilitate removal of material by a wet etchant, otherisotropic etchant, or cleaning solution, without leaving surfaceroughness anomalies that are large enough to affect the performance ofthe resulting structure (e.g., a semiconductor device structure). Such asolution includes, among other things, at least one etch blocker forpreventing material at corners in the film surface from being removed ata significantly faster rate than material is removed from smoother(e.g., more planar) surfaces of the film and, optionally, an etchant orcleaning solution for chemically etching one or more materials.

An etch blocker-containing solution of the present invention may includean etch solution in addition to the etch blocker. The etch solution ofsuch a wet etchant is configured to remove a material of the film. Theetch solution, as well as the concentrations of one or more chemicalsthereof, may be selected based on a variety of known factors, includingits ability to remove the desired material or materials, the rate atwhich it removes the desired material or materials, the conditions inwhich material removal may be effected, the selectivity with which itremoves the desired material or materials over other materials, itscompatibility with photoresist (which may be present when STI shallowtrench isolation structures are recessed, such as in NAND flashfabrication processes), and other factors. Embodiments of a wet etchantof the present invention include an etch solution and etch blocker thatare compatible with one another. For example, the chemical properties(e.g., ionic strength, pH, etc.) of the etch solution may allow the etchblocker to cover (e.g., adsorb to) an anomaly in a surface of astructure or film that is to be etched, and may even facilitate coatingdesired regions of the structure or film with the etch blocker.

Systems and methods according to embodiments of the present inventionare now described with reference to FIGS. 2-8.

As depicted in FIG. 2, a fabrication substrate 100 may be carried by asubstrate holder 120 of a system 1 of an embodiment of the presentinvention as a method according to an embodiment of the presentinvention is effected. As used herein, the term “fabrication substrate”includes, without limitation, full or partial semiconductor (e.g.,silicon, gallium arsenide, indium phosphide, etc.) wafers, asilicon-on-insulator (SOI) type substrates (e.g., silicon-on-ceramic(SOC), silicon-on-glass (SOG), silicon-on-sapphire (SOS), etc.), and thelike. System 1 may also include means for generating pressure waves 130,which are associated with substrate holder 120 in such a way as togenerate pressure waves in a solution 20 that may include a wet etchanton at least a portion of fabrication substrate 100 within substrateholder 120.

Means 130 for generating pressure waves may comprise an ultrasonicvibrator configured to initiate and control amplitude and frequency ofvibrations and having one or more transmission elements (e.g.,transducers) operably coupled to the volume of solution 20 andpositioned to initiate and control the direction, amplitude andfrequency of waves stimulated in solution 20. The vibrator may beoperable to superimpose waves of varying frequency and amplitude tocreate turbulence (eddies, vortices, etc.), in solution 20 to initiate a“scrubbing” effect to selectively remove etch blockers 22 from majorsurfaces of a film on fabrication substrate 100 oriented substantiallyparallel to the major plane thereof.

Turbulence formed by pressure wave generator 130 and solution 20, asreferenced above, acts on fluid in a recess or crevice to a depth ofapproximately 300 Å. Thus, turbulence can be effectively employed toscrub etch blockers, such as surfactants, from an exposed surface of afilm or other structure, while allowing the etch blocker to residewithin the recess or crevice.

In another embodiment, means for generating pressure waves 130 mayinclude a single-wafer spin tool of a type known in the art, which mayinclude apparatus for spraying or otherwise dispensing solution 20 ontoan exposed surface of fabrication substrate 100. One or both of thecentrifugal force generated by spinning and the force with whichsolution 20 is applied to a surface of fabrication substrate 100 mayresult in the selective removal of the etch blocker from exposedsurfaces, while allowing the etch blocker to remain within recessedlocations.

Another embodiment of means for generating pressure waves 130 includes abatch cleaning tool, such as a cleaning tool with a recirculating tankor a spray tool, which cause fluids to move across (substantiallyparallel to) or impact (transverse to) surfaces of a fabricationsubstrate 100 (e.g., by recirculation current or spray) at relativelyhigh velocity. Examples of batch cleaning tools are available from TEL(Tokyo Electron) of Tokyo, Japan, and DNS Electronics of Sunnyvale,Calif. When a batch cleaning tool is employed as a means for generatingpressure waves 130, a surface of fabrication substrate 100 may beexposed to solution 20 while fabrication substrate 100 is within thebatch cleaning tool.

In an embodiment of a method of the present invention, etch blockers 22are introduced into recesses or crevices 12 of an exposed surface 14 ofstructure or film 10 from which material is to be removed, asrepresented in FIG. 3. Without limiting the scope of the presentinvention, etch blockers 22 may be part of, or carried by, a solution20. In other embodiments, etch blockers 22 may be part of a non-etchingsolution, in which case a separate wet etchant may be used inconjunction with the etch blocker 22-containing solution. When astructure or film 10 and recesses or crevices 12 thereof are exposed asolution that includes etch blocker 22, etch blocker 22 may adsorb to ormerely cover surfaces 13 of structure or film 10 that are located withinrecesses or crevices 12.

The introduction of etch blockers 22 onto a structure or film 10 may beeffected in a selective fashion, in which etch blocker 22 is introducedinto recesses or crevices 12 without substantially remaining on smooth(e.g., substantially planar), nonrecessed, exposed surfaces 14 ofstructure or film 10, such as those surfaces oriented substantiallyparallel to the major plane of fabrication substrate 100 (e.g., into aseam of an STI structure). In this regard, and with reference to FIG. 4,any etch blocker 22 present on smooth (e.g., substantially planar),nonrecessed, exposed surfaces 14 of structure or film 10 following theintroduction of etch blocker 22 into recesses or crevices 12 may beremoved. As a nonlimiting example, at least some etch blocker 22 may beremoved from smooth, nonrecessed, exposed surfaces 14 by way of pressurewaves 30. When etch blocker 22 is part of or carried by a solution 20,etch blocker 22 on smooth, nonrecessed, exposed surfaces 14 may beremoved by generating pressure waves 30 (e.g., in the form ofturbulence) within solution 20. Pressure waves 30 (e.g. turbulentmovement of solution 20) may extend or travel in a direction that issubstantially parallel to the smooth, nonrecessed, exposed surface 14from which etch blocker 22 is to be removed. This orientation ofpressure waves 30 minimizes their introduction (e.g., the turbulent flowof solution 20) into recesses or crevices 12, as well as the formationof bubbles within recesses or crevices 12, leaving etch blocker 22within recesses or crevices 12 substantially undisturbed. The amplitudeof pressure waves 30 may also be optimized to facilitate removal of etchblocker 22 from smooth, nonrecessed, exposed surfaces 14 whileminimizing the depth that pressure waves 30 intrude into recesses orcrevices 12.

Without limiting the scope of the present invention, pressure waves 30,in the form of turbulence (e.g., random eddies, vortices, and other flowfluctuations) in solution 20, may be induced by cavitation, sonication,or any other suitable technique 130 for generating pressure waves 30(see FIG. 2) or causing fluid to move across a surface of fabricationsubstrate 100 that are known in to those of ordinary skill in the art.

Material removal or surface cleaning occur as soon as a solution 20 thatincludes a wet etchant or cleaning solution, respectively, contactssurfaces, including smooth, nonrecessed, exposed surfaces 14, ofstructure or film 10, during or after the introduction of etch blocker22 into recesses or crevices 12 and removal of etch blocker 22 fromsmooth, nonrecessed, exposed surfaces 14. In one embodiment, when etchblocker 22 is carried by or is part of a solution 20 that also includesor comprises an etchant 24 (see FIGS. 3 and 4) for removing materialfrom structure or film 10, material removal may occur while the materialis exposed to solution 20. In another embodiment, when solution 20 doesnot include any etchant 24, etchant 24 may be added to solution 20, orsolution 20 may be substantially removed from structure or film 10 assoon as material removal is desired.

As FIGS. 5 and 6 illustrate, upon contacting structure or film 10,etchant 24 removes material from structure or film 10. Etchant 24 isprevented from contacting regions or features of structure or film 10that are covered or coated by etch blocker 22 and, thus, etch blocker 22prevents or hinders the removal of material from these regions. Use ofan etch blocker 22 in his manner facilitates the removal of materialfrom structure or film 10 until substantially no undesirable recesses orcrevices 12 remain in the nonrecessed, exposed surface of structure orfilm 10, as shown in FIG. 7. Removal to the extent depicted in FIG. 7may be effected by exposing structure or film 10 to etchant 24 for apredetermined period of time, at a predetermined temperature, at apredetermined concentration, using a combination of the foregoing, orotherwise, as known to those of ordinary skill in the art.

If further material removal is desired after the point depicted in FIG.7, etch blocker 22 may be substantially removed from structure or film10, such as by the generation of pressure waves 30, as described withreference to FIG. 4, by washing and rinsing processes, as known in theart, or by any other suitable known technique, as shown in FIG. 8.Further material removal may then be effected in any suitable mannerknown in the art (e.g., oxygen (O₂) ashing processes are useful forremoving organic materials, etc.).

In other embodiments, shown in FIGS. 3 and 4, an etch blocker 22′ may benonselectively adsorbed to exposed surfaces 14 of structure of film 10.In such embodiments, etch blocker 22′ may comprise a surface activepolymer, a non-ionic or low ionic strength surfactant, or any othersuitable material. When etch blocker 22′ is used with an etchant thathas a high ionic strength (e.g., a BOE, etc.), the ionic strength of theetchant may compensate for low attractive forces of etch blockers 22′ toexposed surfaces 14. Thus, etch blocker 22′ may nonspecifically adsorbto and coat exposed surfaces 14.

As shown in FIG. 3, an exposed surface 14 of a structure or film 10 thatis to be subjected to material removal (e.g., etching) processes isexposed to an etchant mixture 18 that includes a solution 20 with etchblocker 22′ dispersed therethrough. Etch blocker 22′ may comprise aboutone percent or less of the volume of the components of an etchantmixture, but may comprise as much as about twenty percent of the volumeof the etchant mixture. FIG. 3 illustrates the nonselective adsorptionof etch blocker 22′ to exposed surface 14 and, thus, a coating 23′ ofetch blocker 22′ on exposed surface 14. Coating 23′ acts as a diffusionbarrier that physically impedes the mass transport of reactive etchspecies to exposed surface 14 and the removal of etch by-products fromexposed surface 14. As illustrated, material removal processes are shownin which in which coating 23′ enables an isotropic etchant to removematerial from all areas of exposed surface 14, including regions ofexposed surface 14 with recesses or crevices, at substantially the samerate.

Once a desired amount of material has been removed from structure orfilm 10, etchant mixture 18, including coating 23′, may be removed fromstructure or film 10, as shown in FIG. 4, by any known, suitable process(e.g., by rinsing, washing, etc.).

Solutions, processes, or combinations thereof, of embodiments of thepresent invention may be used in a variety of applications and readilyand cost-effectively incorporated into a variety of existing processes.The solutions, processes, and combinations thereof are particularlyuseful for removing materials in which seams, keyholes, or otherrecesses or crevices are formed following deposition of the materials inrecesses, such as trenches, including during material removal (e.g.,etching) and cleaning processes (e.g., from STI structures, fromconductive contact plugs, etc.). Wet etchants and processes of thepresent invention may be used to remove materials from or from abovestructures or features having at least one dimension of about 50 nm orless.

For example, wet etchants and processes of the present invention may beused to recess the materials (e.g., ozone-tetraethyl orthosilicate(TEOS), etc.) of shallow trench isolation (STI) structures ofsemiconductor devices that include floating NAND gates. As anotherexample, etchants and/or processes according to the present inventionmay be used to wet etch structures (e.g., plugs, etc.) includingtungsten (W), titanium nitride (TiN), polysilicon, or other materials(e.g., wet etchback of 42 level W/TiN contact plugs, etc.).

The following are nonlimiting examples of etchants and that have beenused to recess ozone-TEOS silicon dioxide of STI structures:

EXAMPLE 1

With reference to FIG. 9, semiconductor device structures 101 includingSTI structures 110 with recesses or crevices 112 were exposed for 10(ten) minutes to a BOE etch solution diluted 100:1 and at a pH of about6. Each etch was accompanied by sonication in a lateral direction,substantially parallel to a plane in which a substrate bearing eachsemiconductor device structure 101 was located. In a control, shown inFIG. 9, a semiconductor device structure 101 was exposed just to theetch solution. In addition, semiconductor device structures 101 wereexposed for ten minutes each to the etch solution with 0.1 mM CTAB andwith 1 mM CTAB.

The results of these etches are shown in FIGS. 10 (0.1 mM CTAB) and 11(1 mM CTAB), respectively. It does not appear that the addition of CTABto the etch solution improved the manner in which the etch solutionremoved material from STI structures 110, as the ionic strength of theetch solution likely prevented the CTAB from adsorbing to desiredlocations (i.e., surfaces within recesses or crevices 112 of STIstructures 110). These results indicate that less acidic, and evenbasic, etchants may be suitable for use with cationic surfactants,particularly in situations where cationic surfactants are more likely toadsorb to a material than anionic surfactants.

EXAMPLE 2

In another experiment, silicon dioxide of STI structures 110 includingrecesses or crevices 112 were etched with dilute (100:1) HF at a pH ofabout 1.5 for about 7 (seven) minutes to about 8 (eight) minutes. Eachetch was accompanied by sonication in a lateral direction. The resultsof a control etch (dilute HF alone) are shown in FIG. 12, while theresults of an etch in which 0.01% FS-62 was included are shown in FIG.13.

As shown, the inclusion of FS-62 as an etch blocker prevents isotropicetching at recesses or crevices 112 within STI structures 110.

EXAMPLE 3

In a variation of the experiment set forth in EXAMPLE 2, silicon dioxideof STI structures 110 that included recesses or crevices 112 were etchedwith dilute (100:1) HF at a pH of about 1.5 for about 8 (eight) minutes.Each etch was accompanied by sonication in a lateral direction. Theresults of a control etch are shown in FIG. 14, while the results of anetch in which 0.01% FS-62 was included are shown in FIG. 15.

As shown, the inclusion of FS-62 as an etch blocker prevents isotropicetching at recesses or crevices 112 within STI structures 110.

Although the foregoing description contains many specifics, these shouldnot be construed as limiting the scope of the present invention, butmerely as providing illustrations of some of the presently preferredembodiments. Similarly, other embodiments of the invention may bedevised which do not depart from the spirit or scope of the presentinvention. Features from different embodiments may be employed incombination. The scope of the invention is, therefore, indicated andlimited only by the appended claims and their legal equivalents, ratherthan by the foregoing description. All additions, deletions andmodifications to the invention as disclosed herein which fall within themeaning and scope of the claims are to be embraced thereby.

What is claimed:
 1. A method for isotropic etching, comprising: exposinga structure comprising silicon dioxide and having at least one creviceor recess at an exposed surface thereof to a wet etchant consisting ofhydrogen fluoride, water, and at least one fluorosurfactant, the atleast one fluorosurfactant comprising at least one ofCF₃CF₂CF₂CF₂CF₂CF₂CH₂CH₂SO₃X, where X is H or NH₄, and an ammoniumfluoroalkylsulfonate; and generating pressure waves in the wet etchantto remove the at least one fluorosurfactant from the exposed surface ofthe structure while the at least one fluorosurfactant remains within theat least one crevice or recess.
 2. The method of claim 1, whereinexposing a structure comprising silicon dioxide and having at least onecrevice or recess at an exposed surface thereof to a wet etchantcomprises exposing a silicon dioxide shallow trench isolation structureto the wet etchant.
 3. The method of claim 1, further comprisingselecting the at least one fluorosurfactant based at least in part uponan isoelectric point of the silicon dioxide.
 4. A method for fabricatinga semiconductor device structure, comprising: exposing a film orstructure comprising silicon dioxide and having at least one anomalyextending from a substantially smooth surface thereof to a wet etchantconsisting of hydrogen fluoride, water, and at least onefluorosurfactant, the at least one fluorosurfactant comprising at leastone of CF₃CF₂CF₂CF₂CF₂CF₂CH₂CH₂SO₃X, where X is H or NH₄, and anammonium fluoroalkylsulfonate; and generating pressure waves across asurface of the film or structure.
 5. The method of claim 4, whereingenerating pressure waves across a surface of the film or structurecomprises removing the fluorosurfactant from substantially smoothsurfaces while the fluorosurfactant remains within the at least oneanomaly.
 6. A method for fabricating a semiconductor device structure,comprising: applying an etchant mixture consisting of hydrogen fluoride,water, and at least one fluorosurfactant to an exposed surface of asilicon dioxide structure from which material is to be removed, the atleast one fluorosurfactant comprising at least one ofCF₃CF₂CF₂CF₂CF₂CF₂CH₂CH₂SO₃X, where X is H or NH₄, and an ammoniumfluoroalkylsulfonate and absorbing to surfaces of the silicon dioxidestructure defining at least one crevice or recess therein and enablingremoval of material from all areas of the exposed surface, includingexposed regions of the at least one crevice or recess, at substantiallythe same rate.
 7. The method of claim 6, wherein applying an etchantmixture comprises applying an etchant mixture having a pH of about 1.5.8. The method of claim 6, wherein applying an etchant mixture comprisesapplying an etchant mixture in which the hydrogen fluoride and water arepresent in a ratio of about 1:100.
 9. The method of claim 6, whereinapplying an etchant mixture comprises applying an etchant mixtureincluding at most about one percent, by volume, of the at least onefluorosurfactant.
 10. The method of claim 6, wherein applying an etchantmixture comprises applying an etchant mixture including at most abouttwenty percent, by volume, of the at least one fluorosurfactant.
 11. Themethod of claim 1, wherein generating pressure waves in the wet etchantto remove the at least one fluorosurfactant from the exposed surface ofthe structure while the at least one fluorosurfactant remains within theat least one crevice or recess comprises removing material fromunrecessed surfaces of the structure without removing material fromsurfaces of the structure defining the at least one crevice or recess.12. The method of claim 1, wherein exposing a structure comprisingsilicon dioxide and having at least one crevice or recess at an exposedsurface thereof to a wet etchant comprises exposing a silicon dioxideshallow trench isolation structure having the at least one crevice orrecess therein to a wet etchant consisting of hydrogen fluoride, water,and at least one fluorosurfactant to remove material from unrecessedsurfaces of the silicon dioxide shallow trench isolation structure. 13.The method of claim 1, wherein generating pressure waves in the wetetchant to remove the at least one fluorosurfactant from the exposedsurface of the structure while the at least one fluorosurfactant remainswithin the at least one crevice or recess comprises generating pressurewaves in the wet etchant in a direction substantially parallel to amajor surface of a film that has been conformally deposited to fill atleast one contact hole or trench to remove the at least onefluorosurfactant from unrecessed surfaces of the film while the at leastone fluorosurfactant remains within the at least one crevice or recesslocated over the at least one contact hole or trench.